With the introduction of gunpowder in the 15th century, the once mighty castles fell with relative ease to invaders. However, opposed to popular belief, it wasn't really gunpowders that finished the Castles Age. Most castles could be strengthened to stop even cannonballs and in addition, castle walls were perfect to situate defensive cannons and arquebusiers.

Castles and knights played a central role in medieval warfare during the 12th, 13th and 14th centuries. As knights, castles did not become obsolete after the 15th century. Castles were useful during the 16th century and beyond.

What really stopped the development of new castles and geared warfare towards open-field battles was political changes. With the new political geography, many castles became obsolete and constructing new ones in the frontier resulted extremely expensive. It was far more cost-efficient to attack than to defend.

Many castles became prisons as it wasn't only difficult to get in, but also to get out. The Tower of London and the Bastille are notorious for hosting primarily political prisoners. Many other castles continued to serve for defensive purposes until as late as the 20th century during the Second World War. A relative minority are today used as museums or hotels. Some castles are still inhabited by their owners. Unfortunately, many other castles were destroyed and their stone used for the creation of new buildings. This was especially frequent after the 15th century when a castle was re-captured and, needing stone to construct modern fortifications or to repair damaged buildings outside the castles (such as churches), the castle was destroyed.